The present invention generally relates to apparatus for testing infrared (IR) sensors, and is directed more particularly to apparatus for calibrating black body differential temperature sources that are utilized in testing IR sensors.
Infrared sensors are utilized to produce data based on the thermal signature of the scene being viewed, and are commonly tested relative to differential temperature sources (also referred to as black body sources) such as those commercially available from Electro Optical Industries, Inc., Santa Barbara, Calif.
Differential temperature sources typically include a target plate having an apertured pattern and a controlled plate, with the target plate being closer to the IR imaging system being tested. The temperature difference between the target plate and the controlled plate is controlled pursuant to an input differential temperature setting (i.e., the desired temperature difference between the plates) by a temperature controller, for example by monitoring both plates and leaving the target plate at ambient temperature while controlling the temperature of the controlled plate.
Typically, the temperature controller of a differential temperature source provides an indicated differential temperature information in the form of a human viewable display as well as a data output, for example on a bus conforming to the IEEE 488 standard. However, the relation between the indicated differential temperature and the actual differential temperature may not always be known, and for testing purposes the differential temperature source must be calibrated so that actual differential temperatures can be calculated from indicated differential temperatures.
A known technique for differential temperature source calibration involves utilizing a digital temperature thermometer (DTT) to obtain the actual differential temperatures over a range of indicated differential temperatures. The differences between indicated differential temperature values and the corresponding actual differential temperatures (sometimes referred to as offsets) are utilized as correction factors that can be applied to the readout values. Additionally, collimator efficiency and target emissivity correction factors are calculated separately.
An important consideration with the foregoing technique is that typically the calibration needs to be performed at a location different from the IR sensor testing station which can be disruptive, cause delays, and may require readjustment of the test station optical alignment. Moreover, it requires manual data taking, as well as separate calculations of different correction factors.